With the advent of the information age, composing text with the keys of telecommunication devices has become commonplace. For example, consumers are frequently called upon to spell out words using the keys of a phone pad. Entering text with phones has proven to be awkward, since there are many more letters (26 in the English alphabet) than keys on a standard phone keyboard (generally 12). This necessitates that more than one key be chosen to specify a single letter, thereby resulting in a relatively low text entry rate. The small size of the typical cell phone presents further special challenges, since both the size of the text input area and the number of any additional keys on the cell phone may be limited. While graphical keyboards with alternative key layouts are becoming more popular, the learning curve associated with their text input language can be steep.
FIG. 1 shows a phone layout 20 that includes 12 different keys designated by the numeral 24, which are arranged in 4 (horizontal) rows and 3 (vertical) columns. Ten of the keys 24 have a numeral (0, 1, 2, . . . 9) thereon, denoted by the numeral 28. In addition, the letters (denoted by the numeral 32) of the English alphabet, along with special symbols 36 (* and #), are displayed among the keys 24. The 26 letters of the English alphabet are distributed in alphabetically arranged groups among the numeral-bearing keys 2-9, with each of these groups including at least 3 letters. (The letters S and Z are conventionally assigned to the keys 7 and 9, respectively, although other configurations can be used, e.g., these letters may be displayed on the key 1.) Thus, the letters A, B, and C are assigned to the key 2, the letters D, E, and F are assigned to the key 3, and so on. While the conventional layout shown is not necessarily optimal for the purpose of text input, this layout and ones similar to it have nevertheless become the de facto phone layout standards, and are thus the layouts to which text entry methods and apparatuses conform. (Although the keys 24 shown in FIG. 1 are common to almost all phones, many cell phones include additional keys and switches for which there may be no common standard.)
In order to use one of the standard phone key layouts for text entry, it is necessary to use a technique that distinguishes or “disambiguates” which letter 32 on a given key 24 is the intended one, since a group of letters is generally assigned to a single key. One way of doing this is to algorithmically disambiguate letters with an electronic dictionary of common words (the so-called T-9 technique). In this technique, only one key is tapped for each letter, and a microprocessor or computer in communication with the keypad checks the dictionary to resolve any ambiguity. For example, entering the key sequence 9-WXYZ, 6-MNO, 7-PQRS, 5-JKL, 3-DEF, in that order, would result in the word “WORLD”. However, this method requires a dictionary that may not contain special words (such as people and place names). Additionally, short words consisting of three or four letters can be difficult to disambiguate. Thus, entering the key sequence 4-GHI, 2-ABC, 6-MNO, 3-DEF could correspond to either the word “GAME” or “HAND”. Accordingly, this method may require that the user pay close attention to the text as it is being generated and make any necessary corrections as he or she proceeds, thereby slowing the text entry rate.
Another disambiguation technique is the so-called multi-tap technique. In this technique, the number of taps on a given key specifies the desired letter by the ordering of the letters within the group of letters on the key being tapped. For example, tapping the key 2-abc just once produces the letter A, tapping this key twice produces the letter B, and tapping it three times produces the letter C. Since the number of taps varies from letter to letter, however, some users find this approach counterintuitive and unsatisfactory.
In a two-key sequence method, the user presses two keys consecutively to uniquely determine a letter or symbol. As discussed by M. Silfverberg et al., (“Predicting text entry speed on mobile phones”, Chi 2000, 1-6 Apr. 2000), the keys 1, 2, 3, and 4 can be used to disambiguate the intended letter on a key. For example, 7-PQRS followed by 1 corresponds to the letter P; 7-PQRS followed by the key 2 corresponds to the letter Q; 7-PQRS followed by the key 3 corresponds to the letter R; and 7-PQRS followed by the key 4 corresponds to the letter S. In another two-key sequence method taught by Burrell in U.S. Pat. No. 6,043,761, the keys *, 0, # are used to specify the intended letter within a group of letters. Thus, the letter J is input as 5*, the letter K as 50, and the letter L as 5#. Although these two-key sequence methods are conceptually straightforward, users may be frustrated that some of the two-key sequences involve keys at opposite ends of the keypad, which can result in a slow text entry rate.
Thus, there remains a need for a simple, time-efficient, easy-to-learn text entry method tailored to a standard key layout.